I've had a very hard time connecting my PM 7600 running 7.6.1 (with all updates and add-ons) to my PM G4 running Leopard 10.5.8, using ethernet.
Everything seemed to be set-up properly. Ethernet hub and cables were tested ok. The Leopard machine would get it's IP and afp address, but the 7.6 machine would never get an IP through DHCP and would never connect… Until I switched my OS X Leopard Firewall option to "all incoming connections", and my 7.6 machine instantly received an IP address! I don't know what it involves security-wise, but at least it's working…

Update to my previous post : I can connect to my Leopard G4 afp address only if Shareway Ip is running, which is odd... To sum it up : it won't connect unless Shareway IP is running and Leopard's Firewall authorizes all incoming connections.

The good news is I'm writing this post online in Netscape 4.8 from my OS 7.6.1 computer